Conventionally, there is a device which transmits file documents to a client PC (Personal Computer). This conventional device adds a password to file documents to be transmitted to protect security of the file documents. The client PC receives a password inputted by a user when opening the received file documents. The client PC can open the received file documents when the password added to the file documents and the received password match, and store the file documents. As described above, the conventional device adds a password to file documents from a point of view of protection of security of confidential information or the like included in file documents. The conventional device can secure security which works until file documents are opened. However, in case of the conventional device, file documents including confidential information are stored in a dispersed fashion at a client PC side for a long period of time, and therefore protection of security of file documents is still insufficient.